Just days after two US Navy boats and ten sailors were seized at Farsi Island ahead of President Obama's state-of-the-union address and just days before Tehran will see international sanctions lifted as part of the "historic" nuclear accord, four US hostages have been freed in a prisoner swap between Washington and Tehran.

Among the detainees is Washington Post reporter Jason Rezaian who was famously held for spying after being convicted in a shadowy trial last year and faced up to 20 years in an Iranian prison.

According to FARS, Iran also freed Marine veteran Amir Hekmati and Christian pastor Saeed Abedini, who had been held on a variety of charges.

"All four are duel U.S.-Iranian citizens, according to the semiofficial Mehr and Fars news agencies," WaPo notes, adding that "news of the exchange came as world leaders converged [in Vienna] on Saturday in anticipation of the end of international sanctions against Iran in exchange for significantly curtailing its nuclear program."

Foreign Minister Mohammad Javad Zarif was brimming with optimism when he arrived [in Vienna] earlier in the day and met with Federica Mogherini, the European Union’s foreign policy chief," WaPo says.

“This is a good day for the Iranian people . . . and for the world,” Zarif proclaimed. “What is going to happen today is proof . . . that major problems in the world could be tackled through dialogue, not threats, pressures and sanctions.”

"International sanctions on Iran will be lifted on Saturday when the United Nations nuclear agency declares Tehran has complied with an agreement to scale back its nuclear program," Reuters writes, adding that "'implementation day' of the nuclear deal agreed last year marks the biggest re-entry of a former pariah state onto the global economic stage since the end of the Cold War, and a turning point in the hostility between Iran and the United States that has shaped the Middle East since 1979."

The IAEA is reportedly set to issue a report that confirms Iran has complied with its commitments under the agreement struck last summer. That report will trigger the lifting of sanctions and the return of Iran to the world stage. A joint statement is expected later today.

This comes as US lawmakers push for fresh sanctions on Tehran in connection with two ballistic missile tests the Iranians carried out in October and November, and just weeks after an "incident" in the Strait of Hormuz saw the IRGC conduct a live-fire rocket test within 1,500 yards of a US aircraft carrier.

The deal has ruffled more than a few feathers in Riyadh, where the P5+1 agreement has stoked fears that America's rapprochement with the Iranians marks a shift in US Mid-East policy that could endanger the regional balance of power at a time when relations between the Sunni and Shiite powers have deteriorated markedly. As an aside, Zarif is trolling the Saudis on Twitter as we speak:

#ImplementationDay, it’s now time for all—especially Muslim nations—to join hands and rid the world of violent extremism. Iran is ready.

"Based on an approval of the Supreme National Security Council (SNSC) and the general interests of the Islamic Republic, four Iranian prisoners with dual-nationality were freed today within the framework of a prisoner swap deal," the office of Tehran prosecutor said.

Jason Rezaian, Amir Hekmat, Saeed Abedini and a fourth American-Iranian national who were jailed in Iran on various charges in recent years have all been released.

According o the swap deal, the US has also freed 6 Iranian-Americans who were held for sanctions-related charges..

A senior Iranian legislator citing an IRGC report on Rezaian's case said in October that he has been imprisoned for his attempts to help the US Senate to advance its regime change plots in Iran.

In late July 2014, Iran confirmed that four journalists, including Washington Post correspondent Jason Rezaian, had been arrested and were being held for questioning.

Rezaian's wife Yeganeh Salehi, a correspondent for the United Arab Emirates-based newspaper, the National, was also arrested at that time, but she and two others were released later.

According to the Constitution, the Judiciary is independent from the government in Iran.

Some reports earlier this year had spoken of a potential prisoner swap between Iran and US following the Vienna nuclear deal in July.